THE ACCURACY OF MRI-DETERMINED SYNOVIAL-MEMBRANE AND JOINT EFFUSION VOLUMES IN ARTHRITIS - A COMPARISON OF PRE-ASPIRATION AND POST-ASPIRATION VOLUMES

Magnetic resonance imaging (MRI) of 18 knees of patients with arthriti s was performed before and immediately after arthrocentesis. Pre- and post-aspiration volumes were calculated by adding the outlined areas o f synovium/effusion from a continuous series of gadolinium-DTPA enhanc ed 5 mm transversal T1-weighted MR-images. The difference between MRI- determined and syringe-determined volumes of aspirated joint fluid was 0-7 ml, median 2 ml, corresponding to 0-18%, median 7%, of the pre-as piration effusion volume. Synovial membrane volumes, determined before and after arthrocentesis varied 0-10 ml, median 3 ml (0-17%, median 7 %). No significant systematic misinterpretation of the borderline betw een joint fluid and synovium was found. We conclude that effusion volu mes and in all probability also synovial membrane volumes, can be dete rmined by MRI with a maximal analytical error of approximately 20%. Th e acceptable accuracy of the method encourages further studies of the value of effusion and synovial membrane volumes as markers of the acti vity and/or severity of joint inflammation.